Low level switch for hydraulic brakes



Jan. 17, 1950 J. E. FOX 2,494,802

LOW LEVEL SWITCH FOR HYDRAULIC BRAKES Filed May 3, 194'? HIHIIII m vz/vmxe JAM$ 6. FOX. LQQZ- 5y %a%m;,

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, shortage Patented Jan. 17, 1950 uuirsp STATES rarest 2,494,802 LOW LEVEL SWITCH FOR HYBBATULHC BRAKES James E. Fox, Denver, (Colo. Application May 3, 1947, Serial No. 7 3537.65 1 (Claim. (Kill... Milk-dd) i This invention relates to improvements in devices for indicating a dangerously low level oi brake fluid Ina hydraulic brake fluid reservoir. Hydraulic brakes are now quite universally employed in connection with automotive vehicles.

Such'brakes are dependent for sucessful operation on a suillclent supply of brake fluid to eifect v the transfer 'of force necessary.

'- Although hydraulic brake mechanisms are, as

r a rule, very carefully constructed and as nearly leak proof as possible, experience has shown that small leaks, especially past the piston in the master cylinder, will take place, and the fluid will gradually be dissipated. Service station operators recognizing this, usually check the level of the brake fluid in the brake cylinder reservoir and can thus determine the level conditions in time to remedy the same, providing the loss of the fluid is due to ordinary slow leaks.

In addition to the slight and slow loss of fluid that nearly always takes place, it sometimes hap= pens that the pipes or connections through which the brake fluid is transferred from the master cylinder to the brake operating mechanism spring a leak, in which case the fluid disappears suite rapidly and unless some means is provided to apprise the driver of the fact that there is a of bralse fluid, he may discover this only ;when he tries to apply the brakes and finds that they do not respond. Such cases frequently resultin serious accidents;

"lt is theobject of this invention to produce an attachment that can be readily applied to any existing hydraulic brake mechanism for the purpose of signalling to the driver whenever the level oi the brake fluid in the master cylinder reservoir falls to a dangerously low point, thereby warning him of this dangerous condition in time to prevent the occurrence of an accident.

The invention to which application relates can be most clearly explained and most readily understood when reference is had to the accompanying drawing in which the preferred embodiment thereof has been illustrated, and in which:

Figure 1 is a top plan view of a master cylinder andbrake fluid reservoir showing the improved signalling apparatus in place;

Figure 2 is a section through the brake fluid reservoir taken substantially on line 2-2, Figure 1; and

Figure 3 is a diagram of the wiring connections.

The master cylinder and reservoir that have been illustrated onthe drawing are typical of such apparatus and the embodiment illustrated is therefore intended primarily for use in describing the attachment which is equally applicable to other specifically different constructions, all of which, however, are provided with a cylinder and reservoir in a manner somewhat similar to the one illustrated and which will now be described.

By means of broken lines, applicant has indicated a stationary part of the automobile to which the master cylinderis attached, which part has been identified by reference numeral 5. The master cylinder has been designated by reference numeral t and has been shown in elevation only because its interior construction is old and well lmown. The piston rod has been designated by reference numeral l and this is connected with the brake pedal in the usual manner. In the drawing the brake pedal has been shown by broken lines and indicated by reference numeral 8. The cylinder is closed at its inner end by means of a plug 9 and is provided with two or moretubes it from which suitable conduits er tend to the brake mechanism at the wheels. On top of the brake cylinder is positioned a rectangular container forming a brake fluid reserve reservoir, which has been designated by reference numeral M. The level of the brake fluid has been. indicated by broken line 62. The reservoir has a substantially rectangular cross section in a horizontal plane and is provided with a re= movable cover. it that is secured to the reservoir portion by means of screws i l. The bottom of the reservoir is provided with a hole it that com" municates the interior thereof with the interior of the cylinder. This hole is located towards the left and at such a position that the brake fluid may flow from the reservoir into the cylinder when the piston ill is in its inoperative or withdrawn position.

As above explained, this invention does not relate to the construction of the master cylinder and therefore the description will be limited to such features as appear to be necessary for proper understanding of the signal mechanism to which this invention relates. The master cylinder is provided with a base member l8 that is secured to the stationary part liby means of belts or screws it.

The cover i3 is provided with a fill opening 28 whose inner wall surface is threaded for the reception of a similarly threaded closure .plug M. This plug is of ordinary construction and has a flange 22 that overlaps the cylindrical wall 23 and engages the gasket 24. The closure plug has an upwardly extending square projection 25 by means ofwhich it may be rotated. The cover it, illustrated in this drawing, has been shown as aseaeoe 3 7 provided with an auxiliary flll opening it closed bymeansofapiugl'l. Thisauxiliaryflilopening is not present in the usual construction but serves a useful purpose and is a great convenience whentheusualflllopeningandplugareutilized foroperatingtbesignalinamannerwhichwili now be described.

Plugtl isprovidedwithanaidaiopeningil through which a rod 20 extends. This rod must be of such size that it can slide freely in opening 30. A cork or hollow metal float 30 is secured to the lower end of rod I and rests on the surface of the brake fluid. The float 30 must, of course, have sufllcient buoyancy to lift the rod with its attached parts from the position shown by full linesinl 'lgureiltothatdesignatedbybroken lines and the diameter must be somewhat smaller than the diameter of the flll opening so that it may be readily removed and inserted.

Rod 29 is reversely bent at the top terminating in a downwardly extending end 3| to which a forked switch contact 32 is connected by means of a pivot 33. The ends of forked member l2 terminate in sharp points for a purpose which will hereinafter appear. Secured to the top of plug It is a plate ll of some material that is both electrically insulating and oil resistant. This plate is provided with a rectangular opening I! for the reception of plug II and has secured to its upper surface two concentric rings of electrically conducting metal. The outer ring has been designated by reference numeral 30 and the inner, or smaller ring, has been designated by reference numeral 01. These rings are preferably made from some soft material such as solder or lead and are secured to the insulating plate by means of screws 30. Some of the screws that hold the smaller ring 31 in place are longer than the thickness of plate 3| and engage in threaded holes in plug 2| and therefore serve the double purpose of securing the ring in place and grounding the same to the plug which, in turn, is electrically connected with the automobile frame. The outer ring is of such size that the screws that hold this in place will be positioned outside of flange 22, thereby insulating that ring from the automobile frame. An electrical conductor 30 is connected with the outer ring in the manner shown in Figure 2 and extends to one terminal of a lamp socket, the lamp of which has been designated by reference numeral 40. Conductor 30a connects the other terminal of the lamp with one pole of the storage battery. The other pole of the storage battery is grounded at ll. A switch I! may be provided in conductor No if desired. Since inner ring 31 is grounded at 43, it is evident that if rings 36 and II are interconnected by a conducting member, a circuit will be closed that will cause the lamp 40 to light. The pivoted and forked contact member 32 is intended and so proportioned and designed that it will form an electrical connection between the two rings when the level of the brake fluid sinks below a prede-' termined point, in which case the partswill assume the position shown in Figure 3. If the low level occurs when the automobile is in operation, the movement thereof will cause the contact between rings 00 and TI to be intermittent, thereby producing a flashing of light ll, whichwillbe very apparent both at night and dining the day. Whensuchflashingofthelampoccurathedrher iswarnedtoexaminetheconditionofhisbrakes andtodrivehiscarascautiouslyaspossible.

The forked w member 32 terminates sharppoinistha penetrateanyoilfllmontop ring! soft material, such as lead or solder, any other material of a like nature, the electricalconnectioniseflectedquitereadilybythe weight of the park the float, the rod 20 and the forked contact.

Attention is called to the fact that this signal does not require any change in the present construction and that even the plug ii that is furnished with the usual master cylinder assembly can be employed requiring merely the boring of a central opening 20 and probably a flattening of the upper surface so as to permit a ready attachment of the insulating plate. If the reservoir is not provided with an auxiliary flll opening like that shown, the plug 2| can readily be removed to permit the brake fluid to be increased, whenever occasion requires.

Having described the invention, what is claimed as new is:

A float operated switch for oil level indicators for hydraulic brake fluid reservoirs, comprising, an externally threaded plug having an axial opening, the threads on the plug being so proportioned to threadedly engage internal threads of a flller hole in a top wall of the reservoir a float stem mounted for free reciprocation in the opening and solely guided thereby, a float secured to the lower end of the stem of a size adapted to pass through the filler hole, the upper end of the stem having a lateralb extending portion terminating in a downwardly extending end, a forked contact member pivoted to the downwardly extending end for rocking movement in a substantially radial plane, the ends of the forks having sharp points,

a disk of insulating material secured to the upper end of the plug, in a plane perpendicular to the main portion of the stem and two rings of softv conresilient metal attached to the upper surface of the disk in concentric relation to the opening in the plug, the rings being each positioned underneath a finger of the forked contact, whereby, when the latter moves downwardly in response to a dangerously low level of brake fluid, the rings will be electrically interconnected by the forked contact, the inner ring being electrically connected with the plug and the outer ring insulated therefrom.

JAMIE E. FOX.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS since the latter are 

